Many fish, especially oily, darker-fleshed fish like salmon and herring, are rich in heart-healthy, polyunsaturated, omega-3 fatty acids, but healthful fats are not the only reason to eat fish. Dietary guidelines in the United States encourage adults to eat eight ounces of a variety of fish and seafood each week – roughly two meals’ worth – because of the “total package of nutrients in fish,” which includes lean protein, vitamins A and D as well as B vitamins, and a host of minerals such as iron, iodine, selenium and zinc.

Women who are pregnant or breast-feeding are urged to eat as much as 12 ounces of seafood to improve infant outcomes, but should steer clear of fish that’s high in methyl mercury. (The Food and Drug Administration recommends avoiding king mackerel, tilefish, shark and swordfish and limiting tuna; the nonprofit Environmental Working Group advises against a broader list of fish in its Consumer Guide to Seafood.)

“Fish is very low in saturated fat and low in cholesterol,” said Jennifer McDaniel, a spokeswoman for the Academy of Nutrition and Dietetics, and people who follow a Mediterranean style diet that incorporates seafood appear to be at lower risk for obesity, “but a lot of people don’t think about that and just focus on omega-3s.”

Fish can be a much leaner and lower-calorie source of protein than meat, she noted. A cooked four-ounce portion of cod, for example, contains 26 grams of protein but only one gram of fat and 120 calories, compared with a grilled four-ounce portion of lean T-bone steak, which has 28 grams of protein, 18 grams of fat and 278 calories.

Nutrient content varies depending on the type of fish: Shellfish is especially high in selenium, and saltwater fish is high in iodine, Ms. McDaniel said. The iron in seafood, known as heme iron, is more easily absorbed by the body than the iron from plant sources, and the small bones in sardines are a good source of calcium.

Numerous studies have found that people who eat fish on a regular basis are less likely to die of a heart attack than those who don’t eat it or eat it less than once a month, and a 2006 Harvard review concluded that eating one to two servings of fish rich in omega-3s every week cut the risk of dying of a heart attack by one-third.

Dietary guidelines urge adults to consume 250 milligrams per day of the omega-3 fatty acids EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid). You can get a week’s supply in an eight-ounce portion of salmon or albacore tuna. Other good sources of omega-3s are anchovies, herring, sardines, shad, trout and mussels.